(a) Field of the Invention
This invention relates generally to the commercial refrigeration art, and more particularly to improvements in glass front product merchandisers (so-called xe2x80x9creach-insxe2x80x9d) which hold and display medium and low temperature foods, including specifically doors for such reach-in merchandisers.
(b) Description of the Prior Art
Frozen food merchandisers are designed with the primary objective of maintaining product temperatures in the display area at about 0xc2x0 F. for frozen food and xe2x88x9210xc2x0 F. for ice cream, which in the past have required evaporator coil temperatures in the range of xe2x88x9210xc2x0 F. down to xe2x88x9235xc2x0 F. Medium temperature merchandisers maintain fresh product temperatures generally in the range of 30xc2x0 F. to 40xc2x0 F.
Multi-shelf reach-in merchandisers for storage and display of fresh and frozen food products (including ice cream) provide a generally vertical display of the product for greater visibility and product accessability to shoppers. In order to prevent the escape of cold air into the shopping arena, the display area of the merchandiser is closed by a glass front door. Glass is a poor thermal insulator so the doors are conventionally formed by two or three spaced apart panes of glass, defining one or two air spaces to increase the thermal insulation of the door.
The air spaces must be sealed for maximum insulating effect, and to prevent entry of moisture into these air spaces. Moisture in the air space condenses on the cold glass and obscures viewing of the product in the merchandiser. In the past, sealing of the air space has been accomplished by forming a an xe2x80x9cinsulating glass unitxe2x80x9d or xe2x80x9cIG unitxe2x80x9d (sometimes called a xe2x80x9cglass packxe2x80x9d) which consists of opposing glass panes (called xe2x80x9clightsxe2x80x9d or xe2x80x9clitesxe2x80x9d) separated by a metallic spacer secured by a suitable polymer (e.g., polysulfide, polyisobutylene, etc.). The glass pack is placed in a metal frame to complete the door. Thus, the door assembly process involves two separate steps of forming sealed air spaces, followed by forming a metal frame. Metal is most typically used in the frame and in the spacers because it has a good strength-to-weight ratio. In addition, metal is an excellent moisture barrier and when used as a spacer seals the air space from moisture for many years. However, metal has two important drawbacks when used in reach-in doors. The first is that metal is a poor thermal insulator, and the second is that metal is an excellent electrical conductor.
Conventional attempts to attenuate thermal conduction through the metal in the door generally involve placing barriers in the path of thermal conduction. Others have attempted to partially or entirely replace the metal frame with a polymeric material having a substantially lower thermal conductivity. Examples of such doors are shown in U.S. Pat. Nos. 5,097,642 and 5,228,240. However, it will be noted that in these prior art attempts to reduce the metal used in the doors have not eliminated the metallic spacers, nor have they replaced the need for sealing glass lites before forming the frame.
The electrical conductivity of metal is a hindrance because electrical power is used to heat one or more surfaces of the glass lites in the door. Heating is needed in order to prevent condensation from collecting and obscuring vision through the glass panes of the door. For instance, the moisture in the relatively warm ambient air of the store readily condenses on the outside of the door if it were not heated. Also, when the door is opened moisture condenses on the cold inside glass surface. Without heating, this condensation would not clear quickly and so the view of the product in the merchandiser would be obscured. Typically, heating is achieved by placing a semi-conductive film (e.g., tin-oxide) on the inner surface of the outer glass lite in the door. Bus bars along opposing edges of the lite provide an electrical potential causing a current to flow through the film and produce heat. It is presently necessary to keep the wiring and bus bars supplying the electric power carefully insulated and isolated from the outer metal door frame and the inner metal spacer. This means that a portion of the heating film had to be eliminated at the edge margin where there would be contact with metal. The primary danger occurs when a glass lite is shattered thus exposing the wiring to human contact and electrical shock. Conventionally, expensive electrical circuit breakers, such as ground fault interrupts and fused links, have been used to prevent accidental electrical shock in case of glass breakage.
The method of forming a thermally insulated, transparent door for installation and use on a reach-in merchandiser, in which said door has at least two glass lites and which comprises the steps of: providing a thermally and electrically insulating spacer member having an outer wall portion and an inner separator body portion, forming angled notches in the separator body portion to define the respective corners of first and second glass lites; folding the spacer member at the angled notches around one of the glass lites with the body portion in surface contact with the inner glass lite surface and an edge flange of the outer wall portion in engagement with the adjacent marginal edge thereof, bringing the free end of the spacer member into juxtaposition and securing them together with locking means for holding the spacer member in assembled peripheral contact around the one glass lite, assembling another glass lite in surface contact with the body portion of the spacer member and in spaced relation with the one glass lite, and molding a non-metallic frame of a preselected polyurethane material to peripherally encase the assembled glass lites and spacer member and create an air-tight seal therebetween.
A principal object of the present invention is to provide a method of making a reach-in door for a product display merchandiser which has door and casing improvements, better thermal insulation, better low-glare lighting, safer electrical isolation, secure door hinging and closure features and improved manufacturing.
A more specific object is to provide a method for a reach-in door having low thermal conductivity in which air spaces between glass lites of the doors are effectively sealed upon formation of the molded door frame.
Another object of the invention is to provide a method for a reach-in door which maintains a barrier to moisture entering the air spaces between glass lites.
Another object is to provide a method for a reach-in door which is more thermally insulated and therefore more energy efficient.
Another object is to provide a method for a reach-in door incorporating electrically insulating means simplifying the construction and installation of the door necessary to permit heating of one or more glass lites of the door and to reduce the risk of accidental shock in case of breakage of the lites.
These and other objects and advantages will become apparent hereinafter.